The planarity of a surface of a silicon substrate much effects the characteristics of a device to be formed on, and techniques for making the silicon substrate surface more planar are proposed.
As a technique for flattening the surface of the silicon substrate, for example, the flattening thermal processing which makes thermal processing in a vacuum or a hydrogen atmosphere is known. In this method, the thermal processing is made in a vacuum or a hydrogen atmosphere at about 900 C-1200 C to migrate and rearrange the silicon atoms of the silicon substrate surface for the flatten.
The followings are examples of related: Japanese Laid-open Patent Publication No. 05-243266; Japanese Laid-open Patent Publication No. 07-165410; Japanese Laid-open Patent Publication No. 11-176828; Japanese Laid-open Patent Publication No. 2005-142445; Japanese Laid-open Patent Publication No. 2005-150398; and Japanese Patent No. 2689985.
However, the inventors of the present application have made earnest studies of the relationships between the flatness of the silicon substrate and the device characteristics and have made it clear for the first time that the conventional flattening thermal processing cannot make the atomic level flatness sufficient, and this causes increase of the low-frequency noise.